Hypersensitivity and allergy Flashcards
Define hypersensitivity, allergy and allergen
Hypersensitivity - Undesirable overreaction by a normal immune system
Allergy - Immunological hypersensitivity reaction to allergens
Allergen - A substance that triggers activation of an immune response
How do type 1 hypersensitivity reactions arise?
Stimulation of antigen bound to IgE on an Fc receptor on the surface of mast cells
What are examples of diseases associated with type 1 reactions?
Hayfever, allergic conjunctivitis, Eczema
What do mast cells release when stimulated?
Histamine, cytokines, PGs and LKs
Stimulated by complement cascade usually
Which cells express the Fc receptor for IgE?
Mast cells, basophils and activated eosinophils
What do Th1 cells produce?
IFNy - which then activates macrophages and inhibits Th2 production
What do Th1 cells produce?
IL-4+5 - activates mast cells, B cells anf Eosinophils
IL-10 - Inhibits production of IFNy from Th1 cells
What are the 2ndary effects of mast cell degranulation?
Stomach cramps, vomiting, Diarrhoea (can effect smooth muscle lining stomach)
What are the acute responses of airway hypersensitivity reactions?
Increased mucus production
Inflammatory mediators released
Recruitment of cells from circulation
Smooth muscle contraction
What are the chronic responses of airway hypersensitivity reactions?
Cytokine and eosinophil products damage the airways
What is an extreme case of a type 1 reaction?
Anaphylactic shock - treated with adrenaline to dilate smooth muscle and restore normal blood flow
What are the common treatments of hypersensitivity reactions?
Patch test Diaries Anti-histamines NSAIDs Corticosteroid cream Allergen desensitisation
How do type 2 reactions occur?
via the complement pathway
How do type 3 hypersensitivity reactions occur?
Immune complexes are deposited (joints usually)
How do type 4 hypersensitivity reactions occur?
T-cell mediated reaction
